This invention relates generally to slide fasteners and in particular to a slide fastener of the type having a pair of series of discrete fastener elements attached astride respective longitudinal beaded edges of a pair of carrier tapes.
In the production of slide fasteners of the type described, it is now the common practice to provide discrete fastener elements made of a metal, each of which elements comprises a coupling head and a pair of legs extending therefrom and flared outwardly to assume a substantially, cross-sectionally V-shaped contour. In order to attach the fastener elements to the carrier tape, the legs are arranged astride a longitudinal beaded edge of the tape and then pressed toward each other into gripping engagement with the beaded edge. However, the prior art legs were provided with a smooth peripheral inner wall having oppositely disposed portions in each pair that are adapted to grip the beaded edge of the carrier tape. This has led to the drawback that the fastener elements are liable to tilt relative to and disengage from the beaded edge when repeatedly subjected to severe external stresses tending to loosen the legs gradually out of firm gripping engagement with the beaded tape edge. Furthermore, under these conditions, the fastener elements are prone to be displaced along the longitudinal beaded edge of the tape with the results that the pitch of adjacent fastener elements is disturbed, failing to interlock the opposed stringers in an orderly manner. Various attempts have heretofore been made to explore more effective and secure attachment of the fastener elements to the beaded edge of the carrier tape. One such attempt was to form alternate elongated ridges on and grooves in the peripheral inner wall of the legs, which ridges and grooves extend pitchwise throughout the entire thickness of the element. However, this effort suffered the difficulty that the fastener elements are not fully prevented from being displaced along the longitudinal beaded edge of the tape. Another attempt involved the provision of a groove or recess extending in the peripheral inner wall of the legs and longitudinally of the element. This arrangement, however, cannot eliminate the tendency of the fastener elements to become displaced tiltingly relative to and finally disengaged from the beaded tape edge, and is further disadvantageous in that because the beaded tape edge when gripped by the element legs is bulged into the groove, it is necessary to use extra beading material of high bulk and resiliency to compensate for the room of such groove.